1. Technical Field
The disclosed embodiments generally relate to the field of coatings on a substrate. In particular the disclosed embodiments relate to semi-permanent wear resistant coatings that exhibit lubricious and release properties. While not to be limiting, the coating embodiments disclosed herein are well suited for use in molten glass delivery and molding components.
2. Description of the Related Art
Molded articles such as glass lenses, screen panels for televisions, etc., require refracting surfaces of precise configuration and a high degree of surface smoothness. With respect to other glass articles such as glass bottles, containers, and the like, the requirement for surface smoothness is not as stringent, but there is a common requirement for the molding to be done at high temperatures of about 500° C. or higher. Accordingly, the mold to be used for glass forming must have chemical and physical properties such as mechanical strength, heat resistance, and chemical stability against the high temperature molten glass, as well as other characteristics such as surface roughness, surface precision, and reliable release.
Molten glass is also transported from the melting furnace to the forming operation. Depending on the product the molten glass may move as continuous sheets, ribbons, discrete molten bodies, gobs, and partially formed components or parisons. In order to maintain consistent timing and transportation performance, coatings are applied to the handling component surfaces. Common coatings contain graphite particles in an epoxy resin. These coatings can last from a few days to several weeks of continuous duty. It may be necessary to augment the coatings with oil that is sprayed or swabbed onto surfaces as often as every 30 minutes.
There are several significant disadvantages in lubricating molds or transportation components, either by hand or automatically. Hand swabbing, aside from being hazardous, requires application of lubricant at a time when the cycle of the machine mechanism permits. Mechanized spray units complicate the cycle of the machine and require that the mold parts to be lubricated be made accessible for insertion of a spray nozzle and time allowed for spraying and removal of the nozzle before beginning the forming cycle again.
In the application of a release agent or lubricant to a mold surface by hand or an automated sprayer station, one or more cycles of molding may be missed because of the time required for the swabbing or spraying operation. Sprayer stations add to the cost and maintenance of the molding process. These combine to decrease productivity, increase costs, and may result in non-uniform, excessive or incomplete lubrication of the mold parts.
Several patents describe prior attempts to address these problems. For example, U.S. Pat. No. 5,595,639 teaches coating the inner surface of the glass-forming mold a nickel or nickel-based alloy composition comprising chiefly nickel and graphite granules. U.S. Pat. No. 4,747,864 discloses glass-forming molds coated with an optically smooth titanium nitride surface. U.S. Pat. No. 4,168,961 discloses molds having molding surfaces of a silicon carbide/glassy carbon mixture. U.S. Pat. No. 3,244,497 discloses glass forming mold parts having surfaces coating with refractory nitrides, carbides, oxides, borides and boride complexes. U.S. Pat. No. 4,139,677 proposes a molding surface of silicon carbide or silicon nitride. U.S. Pat. Pub. No. 2003/00005725 teaches coating the mold with a chromium-plated coating film and subsequently a coating containing a silicon compound. U.S. Pat. Nos. 3,936,577 and RE33,767 disclose methods for concomitant particulate diamond deposition in a metal by electroless plating on substrates. U.S. Pat. No. 4,906,532 discloses particulate diamond composite coatings for textile tools by electroless deposition where the diamond has at least two nominal sizes. U.S. Pat. No. 6,309,583 teaches a method of making composite coatings with enhanced thermal properties by electroless deposition that includes diamonds. All of the references listed in this paragraph are incorporated into the present disclosure in their entirety by reference.
In most modern, high-production glass container factories today, there are several types of coatings used for maintaining lubricity and release properties. In most of these coatings, the primary release agent is graphite. Graphite lends itself well to the glass industry because it does not decompose at the temperatures where glass is molten and it maintains a high degree of lubricity over time. However, it is a soft material and is easily abraded away in relatively short periods of time usually minutes to hours.
There is a general need for coatings having improved wear and release properties, and a specific need for such coatings for use in glass mold components.
The disclosure contained herein describes attempts to address one or more of the problems described above.